1. Field of the Invention
The present invention relates to a fuel cell system.
2. Description of the Related Art
Recently, studies have been widely made to develop a fuel-cell stack (hereinbelow, frequently referred to as “fuel cell”), in which a plurality of single cells are stacked as a power supply for a fuel cell vehicle or the like. In the fuel cell, electric power is generated by supplying hydrogen gas (fuel gas) and humidified air (oxidant gas) to an anode side (fuel electrode side) and a cathode side (air electrode side), respectively, of a solid polyelectrolyte membrane (hereinbelow, this membrane is frequently referred to as “electrolyte membrane”) forming a single cell.
Generally, hydrogen gas stored in a high-pressure hydrogen tank or the like is introduced to a reducing valve (pressure regulator) where the pressure of the hydrogen gas is reduced to a predetermined pressure, and then fed to the anode side of the fuel cell. However, the pressure of the hydrogen gas fed to the anode side is still higher than that of the humidified air on the cathode side. In order to adjust the balance in pressure between two sides of the fuel cell, a back-pressure regulating valve is disposed downstream of the fuel cell, which controls the pressure of the humidified air. Introduction of such a valve provides a means to prevent failures that may occur in various devices composing a fuel cell, such as electrolyte membrane (see JP2002-352837A, paragraph 0046 and FIG. 1).
However, even when the back-pressure regulating valve is opened to a predetermined degree, some foreign substance may clog the back-pressure regulating valve or the like and elevate the internal pressure of the fuel cell. As a result, devices such as a back-pressure regulating valve or a single cell composing a fuel cell will suffer stress, which may lead to deterioration or failure of the devices.
Examples of the foreign substances that may cause such a problem include ice and water expelled from the fuel cell by scavenging gas (air having a predetermined pressure) when the fuel cell with the inside thereof being frozen is started up.
Therefore, it would be desirable to provide a fuel cell system which can prevent failure and the like of devices that may be caused by the above-mentioned factors.
Illustrative, non-limiting embodiments of the present invention overcome the above disadvantages and other disadvantages not described above.